The present invention relates to a process for splitting soapstock, comprising the steps of mixing the soapstock with a soap splitting acid, and of separating the acid water phase formed from the oil phase.
Glyceride oils of in particular vegetable origin, such as maize oil, sunflower oil, soybean oil, rapeseed oil, safflower oil, cotton seed oil and the like, are valuable raw materials for the food industries. These oils in crude form are usually obtained from seeds and beans by pressing and/or solvent extraction.
Such crude glyceride oils mainly consist of triglyceride components. However, they generally also contain a significant amount of non-triglyceride components including phosphatides (gums), waxy substances, partial glycerides, free fatty acids, sterolglucosidesand esters thereof, sucrolipids, lipoproteins, colouring materials and small amounts of metals. Depending on the intended use of the oil, many of these impurities have an undesirable effect on the (storage) stability, taste, and colour of later products. It is therefore necessary to refine, i.e. to remove the gums and other components from the crude glyceride oils as much as possible.
In general the first step in the refining of glyceride oils is the so-called degumming step, i.e. the removal of the phosphatides. In a conventional degumming process water is added to the crude gluceride oil to hydrate the phosphatides, which are subsequently removed e.g. by centrifugal separation. Since the resulting degummed oil often still contains unacceptably high levels of `non-hydratable` phosphatides, this water-degumming step is normally followed by chemical treatments with acid and/or alkali to remove the residual phosphatides and to neutralize the free fatty acids (`alkali-refining`). Subsequently, the soapstock so formed is separated from the neutralized oil by centrifugal separation.
Soapstock containing the afore-mentioned non-triglyceride components and has to be split prior to it's disposal in order to recover the fatty acids contained therein, and to obtain an effluent (acid water) containing low levels of total fatty matter (TFM), that is material soluble in ether.
During the splitting of the soapstock using a soap splitting acid, such as sulphuric acid, at pH 2 and a soap splitting temperature of 95.degree. C., an emulsion may be formed. The emulsion formation occurs especially when splitting maize- or sunflower soapstock.
There are several unit operations available to break the emulsions formed. These unit operations comprise filtration, centrifugation, settling during long time periods and a low pH treatment. All these unit operation are cumbersome, because of the corrosive nature of the emulsion (for instance a pH of 4 or lower), whereas due to the large amount of acid used the effluent may require a pre-treatment before disposal.
NL-A-69 17290 discloses a method and an apparatus for continuously splitting of soapstock formed in the alkali refining of crude glyceride oil, in which an inorganic acid is intensively mixed with steam in a Venturi tube, and subsequently the acid steam mixture is intensively mixed with soapstock in a second Venturi tube. The soapstock had a temperature of 80.degree.-95.degree. C. and was passed through a separation zone comprising a packed bed of filling material.
GB-A-1,307,862 discloses a process for treating a solution comprising soapstock, sulphonate salt and an inorganic salt for the recovery of fatty acid and a sulphonate salt solution therefrom. This mixture is acidified at 80.degree. C. to pH 2,5 using sulphoric acid.
U.S. Pat. No. 4,118,407 discloses a process for recovering free fatty acid from aqueous crude soapstock containing saponifiable fatty material comprising a glyceride oil, comprising a saponification zone in which crude soapstock is mixed with an inorganic base and recycled inorganic salt containing neutralized acid water. The saponified soapstock is passed to a acidulation zone in which it is mixed with an inorganic salt at a temperature of between about 80.degree.-95.degree. C. Finally, a free fatty acid stream is separated in a separation zone and neutralized acid water is recycled to the saponification zone.
U.S. Pat. No. 4,671,902 discloses a method for the preparation of fatty acid products from glyceride oil soapstock, in which the soapstock is acidulated with an aqueous mineral acid, and after separation of an aqueous solution the remaining emulsion of fatty material and sludge is dried to a watter content of less than 5% resulting in a breakage of the emulsion. The acidification is carried out at 80.degree.-95.degree. C., at a pH of 3-4, for at least two hours.